Etching method

ABSTRACT

An etching method for etching a silicon oxide film is provided that includes generating a plasma from a gas including a hydrogen-containing gas and a fluorine-containing gas using a high frequency power for plasma generation, and etching the silicon oxide film using the generated plasma. The fluorine-containing gas includes a hydrofluorocarbon gas, and the sticking coefficient of radicals generated from the hydrofluorocarbon gas is higher than the sticking coefficient of radicals generated from carbon tetrafluoride (CF 4 ).

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on and claims the benefit of priorityto Japanese Patent Application No. 2015-250060 filed on Dec. 22, 2015,the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an etching method.

2. Description of the Related Art

Etching methods for etching a silicon oxide film using an etching gasincluding CH₂F₂ gas at low temperatures are known (e.g., see JapaneseUnexamined Patent Publication No. 2015-159308). Japanese UnexaminedPatent Publication No. 2015-159308 describes an etching gas for forminga contact hole pattern having a high aspect ratio.

Also, an etching method is known that involves exciting a gas containinghydrogen gas, hydrogen bromide gas, nitrogen trifluoride gas, and atleast one of hydrocarbon gas, fluorocarbon gas, and hydrofluorocarbongas, and etching a multilayer film in the layering direction from itssurface down to a midpoint position to forma hole in the multilayer film(e.g., see Japanese Unexamined Patent Publication No. 2015-153941).

However, the above-described techniques do not address controlling wherereaction products generated during plasma etching are to be deposited ona mask film through selection of the appropriate combination of gases.Thus, according to the above-described techniques, it is difficult tothe control the position where reaction products are to be deposited onthe mask film by controlling a gas to be added to the etching gas.

SUMMARY OF THE INVENTION

In view of the above-problems of the related art, one aspect of thepresent invention is directed to providing an etching method thatenables etching while adjusting the profile of an opening formed in amask film.

According to one embodiment of the present invention, an etching methodfor etching a silicon oxide film is provided that includes generating aplasma from a gas including a hydrogen-containing gas and afluorine-containing gas using a high frequency power for plasmageneration, and etching the silicon oxide film using the generatedplasma. The fluorine-containing gas includes a hydrofluorocarbon gas,and the sticking coefficient of radicals generated from thehydrofluorocarbon gas is higher than the sticking coefficient ofradicals generated from carbon tetrafluoride (CF₄).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an etching apparatus according to anembodiment of the present invention;

FIG. 2 is a diagram showing example etching results of etching a siliconoxide film using H₂ gas and CF₄ gas;

FIG. 3 is a diagram showing example etching results of etching thesilicon oxide film using H₂ gas and CHF₃ gas according to an embodimentof the present invention;

FIG. 4 is a diagram showing example etching results of etching thesilicon oxide film using H₂ gas and CH₂F₂ gas according to an embodimentof the present invention;

FIG. 5 is a diagram showing example etching results of etching thesilicon oxide film using H₂ gas and CH₃F gas according to an embodimentof the present invention;

FIGS. 6A and 6B are graphs indicating etch rates of the silicon oxidefilm and a mask film when the flow rate of CF₄ gas or CH₂F₂ gas iscontrolled to be constant and the flow rate of H₂ gas is variedaccording to an embodiment of the present invention;

FIGS. 7A-7D are diagrams showing example profiles of an opening formedby an etching method according to an embodiment of the presentinvention; and

FIGS. 8A-8D are diagrams showing example profiles of deposited reactionproducts for controlling the profile of an opening formed by an etchingmethod according to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be describedwith reference to the accompanying drawings. Note that elementsillustrated in the drawings and described below that have substantiallythe same functions and/or features are given the same reference numeralsand overlapping descriptions thereof may be omitted.

[Overall Configuration of Etching Apparatus]

First, the overall configuration of an etching apparatus 1 according toan embodiment of the present invention will be described. FIG. 1 is across-sectional view of the etching apparatus 1 according to the presentembodiment.

The etching apparatus 1 includes a cylindrical processing chamber 10made of aluminum having an alumite-treated (anodized) surface, forexample. The processing chamber 10 is grounded.

A mounting table 17 is arranged within the processing chamber 10. Themounting table 17 may be made of aluminum (Al), titanium (Ti), orsilicon carbide (SiC), for example, and is supported on a support 16 viaan insulating cylindrical holder 14. In this way, the mounting table 17is arranged at a bottom portion of the processing chamber 10.

An exhaust pipe 26 is arranged at the bottom portion of the processingchamber 10 and is connected to an exhaust device 28. The exhaust device28 may include a vacuum pump, such as a turbo-molecular pump or a drypump (not shown). The exhaust device 28 is configured to depressurize aprocessing space within the processing chamber 10 to a predeterminedvacuum level and direct gas within the processing chamber 10 towards anexhaust path 20 and an exhaust port 24 to discharge the gas. A baffleplate 22 for controlling the gas flow is arranged in the exhaust path20.

A gate valve 30 is arranged at a side wall of the processing chamber 10.A wafer W may be loaded into or unloaded from the processing chamber 10by opening/closing the gate valve 30.

A first high frequency power supply 31 for generating plasma isconnected to the mounting table 17 via a matching unit 33, and a secondhigh frequency power supply 32 for drawing ions from within the plasmaonto the wafer W is connected to the mounting table 17 via a matchingunit 34. For example, the first high frequency power supply 31 may beconfigured to apply to the mounting table 17, a first high frequencypower HF (high frequency power for plasma generation) with a firstfrequency (e.g., 60 MHz) that is suitable for generating a plasma withinthe processing chamber 10. The second high frequency power supply 32 maybe configured to apply to the mounting table 17, a second high frequencypower LF (high frequency power for biasing) with a second frequency(e.g. 13.56 MHz) that is lower than the first frequency and is suitablefor drawing ions from the plasma onto the wafer W placed on the mountingtable 17. In this way, the mounting table 17 supports the wafer W andalso acts as a lower electrode.

An electrostatic chuck 40 configured to hold the wafer W by anelectrostatic attractive force is provided on a top surface of themounting table 17. The electrostatic chuck 40 includes an electrode 40 athat is made of a conductive film and is arranged between a pair ofinsulating layers 40 b (or insulating sheets). A DC voltage supply 42 isconnected to the electrode 40 a via a switch 43. The electrostatic chuck40 electrostatically attracts and holds the wafer W by a Coulomb forcethat is generated when a voltage is applied thereto from the DC voltagesupply 42. A temperature sensor 77 that detects the temperature of theelectrostatic chuck 40 is arranged at the electrostatic chuck 40. Inthis way, the temperature of the electrostatic chuck 40 may be measured.

A focus ring 18 is arranged at the outer edge of the electrostatic chuck40 to surround the mounting table 17. The focus ring 18 may be made ofsilicon or quartz, for example. The focus ring 18 is provided to improvein-plane etching uniformity.

A gas shower head 38 is arranged at a ceiling portion of the processingchamber 10. The gas shower head 38 acts as an upper electrode at aground potential. In this way, the first high frequency power from thefirst high frequency power supply 31 is capacitively applied between themounting table 17 and the gas shower head 38.

The gas shower head 38 includes an electrode plate 56 having multiplegas holes 56 a and an electrode support 58 configured to detachably holdthe electrode plate 56. A gas supply source 62 is configured to supplyprocessing gas to the gas shower head 38 from a gas inlet 60 a via a gassupply pipe 64. The processing gas supplied to the gas shower head 38 isdiffused at a gas diffusion chamber 57 to be introduced into theprocessing chamber 10 from the multiple gas holes 56 a. A magnet 66 isarranged to extend annularly or concentrically around the processingchamber 10 so that the plasma generated within a plasma generation spaceof the processing chamber 10 may be controlled by the magnetic force ofthe magnet 66.

A heater 75 is embedded within the electrostatic chuck 40. Note that insome embodiments, the heater 75 may be attached to a backside face ofthe electrostatic chuck 40 instead of being embedded within theelectrostatic chuck 40, for example. A current output by an AC powersupply 44 is supplied to the heater 75 via a feeder. In this way, theheater 75 may be able to heat the mounting table 17.

A coolant path 70 is formed within the mounting table 17. A coolant(hereinafter also referred to as “brine”) supplied from a chiller unit71 may be circulated through the coolant path 70 and coolant circulationpipes 73 to thereby cool the mounting table 17.

With the above-described configuration, the mounting table 17 may beheated by the heater 75 and cooled by the brine that is adjusted to apredetermined temperature and is circulated through the coolant path 70within the mounting table 17. In this way, the temperature of the waferW may be adjusted to a desired temperature. Also, a heat transfer gassuch as helium (He) is supplied between the backside surface of thewafer W and the top surface of the electrostatic chuck 40 through a heattransfer gas supply line 72.

A control unit 50 is configured to control the individual components ofthe etching apparatus 1, such as the exhaust device 28, the AC powersupply 44, the DC voltage supply 42, the switch 43 for the electrostaticchuck, the first high frequency power supply 31, the second highfrequency power supply 32, the matching units 33 and 34, a heat transfergas supply source (not shown), the gas supply source 62, and the chillerunit 71. The control unit 50 also acquires a sensor temperature detectedby a temperature sensor 77 attached to the backside surface of theheater 75. Note that the control unit 50 may be connected to a hostcomputer (not shown).

The control unit 50 includes a CPU (Central Processing Unit) 51, a ROM(Read Only Memory) 52, a RAM (Random Access Memory) 53, and an HDD (HardDisk Drive) 54. The CPU 51 executes a plasma process, such as etching,according to various recipes stored in a storage unit that may beimplemented by the ROM 52, the RAM 53, or the HDD 54, for example. Notethat the storage unit also stores various types of data, such as a datatable (described below). The control unit 50 is configured to controlthe temperatures of a heating mechanism implemented by the heater 75 anda cooling mechanism implemented by brine, for example.

When performing an etching process using a plasma generated by theetching apparatus 1 having the above-described configuration, the gatevalve 30 is opened, and a wafer W is loaded into the processing chamber10 and placed on the electrostatic chuck 40. After the wafer W isloaded, the gate valve 30 is closed. Then, the internal pressure of theprocessing chamber 10 is reduced to a predetermined pressure by theexhaust device 28. Then, a voltage from the DC voltage supply 42 isapplied to the electrode 40 a of the electrostatic chuck 40 so that thewafer W may be electrostatically attracted to the electrostatic chuck40.

Then, a predetermined gas is introduced into the processing chamber 10from the shower head 38, and the first high frequency power HF forplasma generation with a predetermined power is applied to the mountingtable 17. The first high frequency power HF causes ionization anddissociation of the gas that has been introduced into the processingchamber 10 to thereby cause plasma generation within the processingchamber 10. The wafer W is etched by ions and radicals included in thegenerated plasma. Also, the second high frequency power LF for biasingmay be applied to the mounting table 17 in order to draw ions in theplasma towards the wafer W. After the plasma etching is completed, thewafer W is unloaded from the processing chamber 10.

[Etching Method]

In the following, an etching method for etching a wafer W using theetching apparatus 1 having the above-described configuration accordingto one embodiment of the present invention is described with referenceto FIGS. 2-5. Note that an initial state of a layered film is shown atthe leftmost side of FIGS. 2-5. Specifically, a silicon oxide (SiO₂)film 200, a silicon nitride (SiN) film 190, and a polysilicon mask film180 are stacked on the wafer W to form the layered film subject toetching. Note that when the etch rate (hereinafter also referred to as“E/R”) of the silicon oxide film 200 increases, the etch rate of themask film 180 decreases relative to the etch rate of the silicon oxidefilm 200 such that a hole with a high aspect ratio may be formed in thesilicon oxide film 200. In this case, the etching profile can beadjusted to a desired profile by controlling the profile of the maskfilm 180.

Thus, in an etching method according to an embodiment of the presentinvention, etching is performed while adjusting the profile of anopening formed in the mask film 180. At this time, the temperature ofthe chiller (chiller unit) is set to −60° C. such that the temperatureof the wafer W may be controlled to be less than or equal to −35° C.,and the silicon oxide film 200 is etched at a high etch rate under suchextremely low temperature environment. The wafer W may be a siliconwafer, for example. The mask film 180 is preferably made of polysiliconor tungsten (W) but may also be an organic film, an amorphous carbonfilm, or a titanium nitride film, for example.

In the following, example etching results that were obtained when apolysilicon film was used as the mask film 180 are described.

<Process Conditions 1 (FIG. 2)>

Chiller −60° C. Temperature Gas Hydrogen (H₂)/Carbon Tetrafluoride (CF₄)Gas Flow Rate H₂ Varied/CF₄ Constant First High 2500 W, Continuous WaveFrequency Power HF Second High 4000 W, Pulse Wave (Frequency: 5 kHz),Frequency Power Duty Cycle: 50% (Effective LF Value of Second HighFrequency Power LF: 2000 W)

Under the above process conditions 1, a plasma was generated from H₂ gasand CF₄ gas, and the generated plasma was used to etch the silicon oxidefilm 200 via the mask film 180 and the silicon nitride film 190. In thisprocess, the flow rate of CF₄ gas was controlled to be constant, and theflow rate of H₂ gas was controlled to be 0 sccm in (a) of FIG. 2, 50sccm in (b) of FIG. 2, 100 sccm in (c) of FIG. 2, 150 sccm in (d) ofFIG. 2, and 300 sccm in (e) of FIG. 2.

As a result, the mask selectivity (etch rate of silicon oxide film200/etch rate of mask film 180) was 1.0 in (a) of FIG. 2, 9.0 in (b) ofFIG. 2, 6.9 in (c) of FIG. 2, 8.0 in (d) of FIG. 2, and 4.1 in (e) ofFIG. 2. It can be appreciated from these results that higher maskselectivity can be achieved by including a hydrogen-containing gas, suchas H₂ gas, in a fluorine-containing gas as compared with the case of notincluding a hydrogen-containing gas in the fluorine-containing gas.

<Process Conditions 2 (FIG. 3)>

Chiller −60° C. Temperature Gas Hydrogen (H₂)/Fluoroform (CHF₃) Gas FlowRate H₂ Varied/CHF₃ Constant First High 2500 W, Continuous WaveFrequency Power HF Second High 4000 W, Pulse Wave (Frequency: 5 kHz),Frequency Power Duty Cycle: 50% (Effective LF Value of Second HighFrequency Power LF: 2000 W)

Under the above process conditions 2, a plasma was generated from H₂ gasand CHF₃ gas, and the generated plasma was used to etch the siliconoxide film 200 via the mask film 180 and the silicon nitride film 190.In this process, the flow rate of CHF₃ gas was controlled to be 0 sccmin (a) of FIG. 3, 25 sccm in (b) of FIG. 3, 50 sccm in (c) of FIG. 3,and 100 sccm in (d) of FIG. 3.

As a result, the mask selectivity was 9.7 in (a) of FIG. 3, 16.9 in (b)of FIG. 3, 12.8 in (c) of FIG. 3, and 9.5 in (d) of FIG. 3. It can beappreciated from these results that the amount of reaction productsdeposited on the mask film 180 increases and the mask selectivityincreases when the etching gas is switched from a combination of H₂ gasand CF₄ gas to a combination of H₂ gas and CHF₃ gas.

<Process Conditions 3 (FIG. 4)>

Chiller −60° C. Temperature Gas Hydrogen (H₂)/Difluoromethane (CH₂F₂)Gas Flow Rate H₂ Varied/CH₂F₂ Constant First High 2500 W, ContinuousWave Frequency Power HF Second High 4000 W, Pulse Wave (Frequency: 5kHz), Frequency Duty Cycle: 50% (Effective Power LF Value of Second HighFrequency Power LF: 2000 W)

Under the above process conditions 3, a plasma was generated from H₂ gasand CH₂F₂ gas, and the generated plasma was used to etch the siliconoxide film 200 via the mask film 180 and the silicon nitride film 190.In this process, the flow rate of CH₂F₂ gas was controlled to beconstant, and the flow rate of H₂ gas was controlled to be 0 sccm in (a)of FIG. 4, 50 sccm in (b) of FIG. 4, 100 sccm in (c) of FIG. 4, and 200sccm in (d) of FIG. 4.

As a result, the mask film 180 was not etched in (a) of FIG. 4, therebymaking the mask selectivity infinite. Also, the mask selectivity was22.7 in (b) of FIG. 4, 20.6 in (c) of FIG. 4, and 26.2 in (d) of FIG. 4.It can be appreciated from these results that the mask selectivity uponetching the silicon oxide film 200 can be increased by switching theetching gas from a combination of H₂ gas and CF₄ gas to a combination ofH₂ gas and CH₂F₂ gas.

<Process Conditions 4 (FIG. 5)>

Chiller −60° C. Temperature Gas Hydrogen (H₂)/Monofluoromethane (CH₃F)Gas Flow Rate H₂ Varied/CH₃F Constant First High 2500 W, Continuous WaveFrequency Power HF Second High 4000 W, Pulse Wave (Frequency: 5 kHz),Frequency Duty Cycle: 50% (Effective Power LF Value of Second HighFrequency Power LF: 2000 W)

Under the above process conditions 4, a plasma was generated from H₂ gasand CH₃F gas, and the generated plasma was used to etch the siliconoxide film 200 via the mask film 180 and the silicon nitride film 190.In this process, the flow rate of CH₃F gas was controlled to beconstant, and the flow rate of H₂ gas was controlled to 0 sccm in (a) ofFIG. 5, 25 sccm in (b) of FIG. 5, 50 sccm in (c) of FIG. 5 (c), and 100sccm in (d) of FIG. 5.

As a result, the mask selectivity was 18.0 in (a) of FIG. 5, 13.7 in (b)of FIG. 5, 12.9 in (c) of FIG. 5, and 21.8 in (d) of FIG. 5. It can beappreciated from these results that the mask selectivity upon etchingthe silicon oxide film 200 can be increased by switching the etching gasfrom a combination of H₂ gas and CF₄ gas to a combination of H₂ gas andCH₃F gas.

Based on the above, when polysilicon is used as the mask film 180, themask selectivity upon performing etching can be increased by adding atleast one of CHF₃ gas, CH₂F₂ gas, and CH₃F gas to an etching gasincluding a hydrogen-containing gas and a fluorine-containing gas ascompared to the case of supplying only H₂ gas and CF₄ gas. For example,by adding at least one of CHF₃ gas, CH₂F₂ gas, and CH₃F gas to anetching gas including H₂ gas and CF₄ gas, the mask selectivity can beincreased to at least 5, and more preferably to at least 9.

Further, in an etching method according to one embodiment, H₂ gas may besupplied as an example of a hydrogen-containing gas, and CF₄ gas may besupplied as an example of a fluorine-containing gas. Also, H₂O isproduced as a reaction product as a result of the silicon oxide film 200being etched by the H₂ gas contained in the etching gas. According to ageneral vapor pressure curve, H₂O has a relatively low saturated vaporpressure. Note that liquid and vapor can coexist along the vaporpressure curve. Accordingly, when the temperature of the chiller is setto an extremely low temperature of about −60° C., H₂O on the surface ofthe silicon oxide film 200 may presumably be saturated to some extentand exist in the form of liquid. The liquid existing on the surface ofthe silicon oxide film 200 as reaction products also include HF-basedradicals produced by a reaction from CF₄ gas. As a result, hydrofluoricacid (HF) is generated by the HF-based radicals and H₂O (water). In thisway, etching may be promoted mainly by a chemical reaction resultingfrom the hydrofluoric acid (HF) being dissolved in water at the surfaceof the silicon oxide film 200, and the etch rate may be substantiallyincreased as a result. Thus, in the etching method according to thepresent embodiment, etching of the silicon oxide film 200 may not besubstantially hampered even when at least one of CHF₃ gas, CH₂F₂ gas,and CH₃F gas is added to an etching gas including H₂ gas and CF₄ gas.That is, in the etching method according to an embodiment of the presentinvention, etching of the silicon oxide film 200 is promoted by actionsof liquid hydrofluoric acid existing on the surface of the silicon oxidefilm 200 under a low temperature environment in which the temperature ofthe wafer W is controlled to be less than or equal to −35° C., and inthis way, a high etch rate may be maintained.

Note that according to the above process conditions 1-4, the second highfrequency power LF is output in the form of a pulse wave. In thefollowing, the on-time of the second high frequency power LF is referredto as “Ton”, and the off-time of the second high frequency power LF isreferred to as “Toff”. In this case, a pulse wave of the second highfrequency power LF with a frequency of 1/(Ton+Toff) is applied. Also,the duty cycle of the second high frequency power LF, corresponding tothe ratio of the on-time Ton with to the total time of the on-time Tonand the off-time Toff, may be expressed as Ton/(Ton+Toff).

According to the above etching results, by outputting the second highfrequency power LF as a pulse wave, heat input from plasma may besuppressed during the off-time Toff of the second high frequency powerLF, and in this way, a temperature increase in the wafer W may beprevented to thereby improve temperature controllability. As a result,the temperature of the wafer W may be controlled to be less than orequal to −35° C., and the silicon oxide film 200 may be etched at a highetch rate in a low temperature environment.

Note that in some embodiments, not only the second high frequency powerLF but also the first high frequency power HF may be output as a pulsewave, for example. Also, in some embodiments, the second high frequencypower LF may not be applied during the etching process, and only thefirst high frequency power HF may be applied, for example. In the casewhere the second high frequency power LF is not applied, the highfrequency power for biasing is turned off such that the deposition ofreaction products on the mask film 180 upon etching the silicon oxidefilm 200 can be promoted.

[Etching Results when Using Tungsten as Mask Film]

In the following, example etching results that were obtained in a casewhere tungsten (W) was used in place of polysilicon as the mask layer180 are described. In the present embodiment, a tungsten (W) blanket (“Wblanket”) and the silicon oxide film 200 were etched.

FIGS. 6A and 6B are graphs indicating the etch rate of the silicon oxidefilm 200 (“Ox E/R”) on the vertical axis on the left side and the etchrate of the W blanket (“W Blanket E/R”) on the vertical axis on theright side. The horizontal axis of FIG. 6A represent the flow rate of H₂gas in a case where the flow rate of CF₄ gas is controlled to beconstant and the flow rate of H₂ gas is controlled to vary. Thehorizontal axis of FIG. 6B represent the flow rate of H₂ gas in a casewhere the flow rate of CH₂F₂ gas is controlled to be constant and theflow rate of H₂ gas is controlled to vary. Process conditions other thanthose related to the etching gas were as follows.

Chiller −60° C. Temperature First High 2500 W, Continuous Wave FrequencyPower HF Second High 4000 W, Pulse Wave (Frequency: 5 kHz), FrequencyPower Duty Cycle: 50% (Effective LF Value of Second High Frequency PowerLF: 2000 W)

By referring to the etching results of FIGS. 6A and 6B, it can beappreciated that the etch rate of the silicon oxide film 200 issufficiently low relative to the etch rate of the tungsten (W) blanketregardless of whether CF₄ gas is used or CH₂F₂ gas is used, andregardless of the flow rate of H₂ gas. Also, as can be appreciated fromthe etching results of FIG. 6B, a high mask selectivity (at least 10)can be achieved by using a gas including H₂ gas and CH₂F₂ gas as anetching gas and using tungsten (W) as the mask film 180.

[Profile Control of Opening in Silicon Oxide Film]

In the following, profile control of the opening formed in the siliconoxide film 200 using a hydrofluorocarbon gas is described with referenceto FIGS. 7A-7D. FIG. 7A illustrates an initial state of the siliconoxide film 200. Note that there is no mask film arranged on top of thesilicon oxide film 200 in FIG. 7A. The silicon oxide film 200 has a holeformed therein. In the present example, etching was performed under thefollowing process conditions.

Gas FIG. 7B: H₂/CF₄ FIG. 7C: H₂/CH₂F₂ First High Frequency Power 2500 W,Continuous HF Wave Second High Frequency Power Not Applied LF

It can be appreciated from FIGS. 7B and 7C that reaction products aregradually deposited on the silicon oxide film 200 by performing etchingunder the above process conditions. In FIG. 7B, reaction products 202are deposited on the silicon oxide film 200 to a certain height aftertime t1, and reaction products 202 are further deposited on thedeposited reaction products 202 after time t2 (t2>t1).

Similarly, in FIG. 7C, reaction products 203 are deposited on thesilicon oxide film 200 to a certain height after time t3, and reactionproducts 203 are further deposited on the deposited reaction products203 after time t4 (t4>t3, t4<t2). Also, it can be appreciated that theprofile of the reaction products 202 shown in FIG. 7B and the profile ofthe reaction products 203 shown in FIG. 7C are different. Specifically,the narrowest portion (wd1) of the hole formed in the reaction product203 is positioned higher relative to the position of the narrowestportion (wd2) of the hole formed in the reaction products 202. That is,the reaction products 203 tend to be deposited towards the top side ofthe hole as compared with the reaction products 202.

Further, note that although FIG. 7B and FIG. 7C are cross-sections ofthe reaction products 202 and the reaction products 203 when they havebeen deposited up to the same height, the deposition rate of thereaction products 203 is higher than the deposition rate of the reactionproducts 202.

The reaction products 202 are formed by the deposition of CF₃ radicals(CF₃*) within the plasma generated from the CF₄ gas of the etching gasincluding H₂ gas and CF₄ gas supplied to the processing chamber 10. Onthe other hand, the reaction products 203 are formed by the depositionof CH₂F radicals (CH₂F*) and CHF₂ radicals (CHF₂*) within the plasmagenerated from the CH₂F₂ gas of the etching gas including H₂ gas andCH₂F₂ gas supplied to the processing chamber 10.

Note that the sticking coefficient of CF₃ radicals is lower than thesticking coefficients of CH₂F radicals and CHF₂ radicals. Thus, the CF₃radicals with the lower sticking coefficient are more likely to traveldeeper into the hole before sticking to a side wall face of the hole,for example. On the other hand, the CH₂F radicals and the CHF₂ radicalswith higher sticking coefficients are more likely to stick to a sidewall face toward the opening of the hole (towards the top side of thehole) or on top of the deposited reaction products, for example. As aresult, the reaction products 202 are more easily deposited on a sidewall face towards the deeper side of the opening of the hole as comparedwith the reaction products 203, and the reaction products 203 are moreeasily deposited on a side wall face near the opening (top side) of thehole or on top of the deposited reaction products as compared with thereaction products 202.

Also, because the sticking coefficients of CH₂F radicals and CHF₂radicals are higher than the sticking coefficient of CF₃ radicals, thedeposition rate of the reaction products 203 is higher than thedeposition rate of the reaction products 202. As a result, higher maskselectivity can be achieved when the reaction products 203 are generatedby supplying the etching gas including H₂ gas and CH₂F₂ gas as comparedwith the case where the reaction products 202 are generated by supplyingthe etching gas including H₂ gas and CF₄ gas. Additionally, the reactionproducts 203 that are generated upon supplying the etching gas includingH₂ gas and CH₂F₂ gas are more easily deposited near the opening (topside) of the hole and on top of deposited reaction products as comparedwith the reaction products 202 that are generated upon supplying theetching gas including H₂ gas and CF₄ gas. Therefore, the profile of thehole formed in the deposited reaction products 203 may be more easilycontrolled to have a substantially vertical configuration as comparedwith the case of controlling the profile of the hole formed in thedeposited reaction products 202 (see FIG. 7D).

Based on the above, in an etching method according to an embodiment ofthe present invention, a plasma may be generated from H₂ gas, CF₄ gas,and CH₂F₂ gas using the first high frequency power HF for plasmageneration, and the generated plasma may be used to etch the siliconoxide film 200. In this case, radicals generated from the CH₂F₂ gas hasa higher sticking coefficient as compared with the sticking coefficientof the radicals generated from the CF₄ gas. Thus, the profile of thereaction products 203 deposited on the mask film 180 may be controlledby controlling the flow rates of the CF₄ gas and the CH₂F₂ gas, forexample. In this way, fine adjustments may be made to the profile of theopening forming in the mask film 180 while performing plasma etching tothereby control the hole etched in the silicon oxide film 200 to have amore vertical configuration, for example.

[Types of Hydrofluorocarbon Gas]

In etching methods according to embodiments of the present invention,the gas supplied along with H₂ gas and CF₄ gas is not limited to CH₂F₂gas and may be some other type of hydrofluorocarbon gas. Note, however,that the sticking coefficient of radicals generated from thehydrofluorocarbon gas has to be higher than the sticking coefficient ofradicals generated from the fluorine-containing gas.

For example, in an etching method according to one embodiment, at leastthree types of gases are used, including H₂ gas and CF₄ gas, and ahydrofluorocarbon gas, which may be at least one of CH₂F₂ gas, CH₃F gas,and CHF₃ gas, for example. In some embodiments, two or more types ofhydrofluorocarbon gases may be added to the H₂ gas and CF₄ gas, forexample. In such case, further fine adjustments may be made to theprofile of the reaction products 203 deposited on the mask film 180 bycontrolling the respective flow rates of the plurality of types ofhydrofluorocarbon gases added to the H₂ gas and CF₄ gas, for example.

Also, in an etching method according to one embodiment of the presentinvention, a step of performing plasma etching by supplying H₂ gas andCF₄ gas, and a step of performing plasma etching by supplying H₂ gas,CF₄ gas, and a hydrofluorocarbon gas may be alternately executed.

[Etching Results]

FIGS. 8A-8D illustrate etching results obtained by implementing etchingmethods according to embodiments of the present invention under theabove process conditions using different types of hydrofluorocarbongases and different flow rates as indicated below. Note that in FIGS.8A-8D, the etching gases were supplied for the requisite time (i.e., 96sec, 60 sec, 39 sec, and 30 sec) such that reaction products would bedeposited up to the same height.

FIG. 8A: H₂/CF₄=150 sccm/100 sccm

FIG. 8B: H₂/CHF₃=100 sccm/100 sccm

FIG. 8C: H₂/CH₂F₂=100 sccm/100 sccm

FIG. 8D: H₂/CH₃F=0 sccm/100 sccm

As shown in FIGS. 8A-8D, reaction products 202, 204, 203, and 205 wererespectively deposited on the silicon oxide film 200 by performingetching while maintaining the temperature of the wafer W to a lowtemperature less than or equal to −35° C. It can be appreciated fromthese results that the reaction products 203-205 that are generated uponperforming etching using a gas including H2 gas and at least one type ofhydrofluorocarbon gas (CH₂F₂ gas, CH₃F gas, or CHF₃ gas) are more likelyto be deposited on the top side of the opening formed in the reactionproducts as compared with the reaction products 202 that are generatedupon performing etching using a gas containing H2 gas and CF₄ gas. Thatis, the reaction products 203-205 are less likely to be deposited on aside wall face of the opening, and as such, the profile of the openingcan be controlled to have a more vertical configuration.

Also, with respect to the deposition rate, the highest deposition ratewas achieved in FIG. 8D where the etching gas H₂/CH₃F was supplied at0/100 sccm, followed by FIG. 8C where the etching gas H₂/CH₂F₂ wassupplied at 100/100 sccm, and then FIG. 8B where the etching gas H₂/CHF₃was supplied at 100/100 sccm. It can be appreciated from the above thatthe deposition rate becomes higher as the number x of H atoms in thehydrofluorocarbon gas CH_(x)F_(y) increases, and the mask selectivityalso increases in this case.

As described above, according to an aspect of an etching method of thepresent embodiment, by adding to the etching gas including H₂ gas andCF₄ gas, a hydrofluorocarbon gas that generates radicals with a stickingcoefficient that is higher than the sticking coefficient of radicalsgenerated from a fluorine-containing gas, etching can be performed whileadjusting the profile of an opening formed in the mask film 180. In thisway, the etching profile of the silicon oxide film 200 arranged underthe mask film 180 may be controlled to have a more verticalconfiguration.

Note that CF₄ gas is an example of a first fluorine-containing gas.Hydrofluorocarbon gas is an example of a second fluorine-containing gas.The second fluorine-containing gas may be at least one ofdifluoromethane (CH₂F₂) gas, monofluoromethane (CH₃F) gas, andfluoroform (CHF₃) gas, for example.

Although an etching method according to the present invention have beendescribed above with respect to certain illustrative embodiments, theetching method according to the present invention is not limited to theabove embodiments, and various modifications and improvements may bemade within the scope of the present invention. Also, features of theembodiments described above may be combined to the extent practicable.

For example, the etching method according to the present invention isnot limited to being applied to a capacitively coupled plasma (CCP)etching apparatus as represented by the etching apparatus 1 but may alsobe implemented in other various types of plasma processing apparatuses.Examples of other types of plasma processing apparatuses include aninductively coupled plasma (ICP) processing apparatus, a plasmaprocessing apparatus using a radial line slot antenna, a helicon waveplasma (HWP) processing apparatus, an electron cyclotron resonanceplasma (ECR) processing apparatus, and the like.

Also, although a semiconductor wafer W is described above as an exampleobject to be etched, the etching method according to the presentinvention may also be implemented on a substrate used in a liquidcrystal display (LCD) or a flat panel display (FPD), a photomask, a CDsubstrate, or a printed circuit board, for example.

What is claimed is:
 1. An etching method for etching a silicon oxidefilm, the etching method comprising: generating a plasma from a gasincluding a hydrogen-containing gas and a fluorine-containing gas usinga high frequency power for plasma generation; and etching the siliconoxide film using the generated plasma; wherein the fluorine-containinggas includes a hydrofluorocarbon gas; and wherein a sticking coefficientof radicals generated from the hydrofluorocarbon gas is higher than asticking coefficient of radicals generated from carbon tetrafluoride(CF₄).
 2. The etching method according to claim 1, wherein thehydrofluorocarbon gas includes at least one of difluoromethane (CH₂F₂)gas, monofluoromethane (CH₃F) gas, and fluoroform (CHF₃) gas.
 3. Anetching method for etching a silicon oxide film, the etching methodcomprising: generating a plasma from a gas including ahydrogen-containing gas, a first fluorine-containing gas, and a secondfluorine-containing gas using a high frequency power for plasmageneration; and etching the silicon oxide film using the generatedplasma; wherein the second fluorine-containing gas includes ahydrofluorocarbon gas; and wherein a sticking coefficient of radicalsgenerated from the hydrofluorocarbon gas is higher than a stickingcoefficient of radicals generated from the first fluorine-containinggas.
 4. The etching method according to claim 3, wherein the etching isperformed in a low temperature environment in which a temperature of awafer is less than or equal to −35° C.
 5. The etching method accordingto claim 3, wherein the hydrogen-containing gas is hydrogen (H₂) gas;the first fluorine-containing gas is carbon tetrafluoride (CF₄) gas; andthe second fluorine-containing gas includes at least one ofdifluoromethane (CH₂F₂) gas, monofluoromethane (CH₃F) gas, andfluoroform (CHF₃) gas.
 6. The etching method according to claim 3,wherein the silicon oxide film is etched via a mask film; and when themask film comprises tungsten (W), a mask selectivity is greater than orequal to
 10. 7. The etching method according to claim 3, wherein thesilicon oxide film is etched via a mask film; and when the mask filmcomprises polysilicon, a mask selectivity is greater than or equal to 5.